In mobile telecommunications, a subscriber is often identified by a Mobile Subscriber Integrated Services Digital Network-Number (MSISDN) and an International Mobile Subscriber Identity (IMSI). The MSISDN is used to route calls to a user equipment (UE) of the subscriber. The IMSI identifies a subscriber to a telecommunications network and typically is permanently associated with a Universal Integrated Circuit Card (UICC), such as a Subscriber Identity Module (SIM) or Universal Subscriber Identity Module (USIM), that is inserted into the UE. With the introduction of IMS, the UICC has been extended to include another security profile called the ISIM (IMS Subscriber Identity Module (ISIM). The MSISDN typically is bound to the IMSI by a service provider when the subscription is purchased for service from a cellular service provider.
Many modern telecommunication systems are moving toward using an Internet Protocol Multimedia Subsystem (IMS), which is an architectural framework for delivering multimedia services over Internet Protocol (IP). IMS aims to provide all mobile telecommunications over IP. For example, applications such as Voice over Long Term Evolution (VoLTE), Video over Long Term Evolution (ViLTE), Short Message Service (SMS), Multimedia Messaging Service (MMS), Mission Critical Push To Talk (MCPTT), and Rich Communication Systems (RCS) all rely on IMS.
A subscription on IMS is identified by an IP multimedia private identity (IMPI) and can have one or more IP multimedia public identities (IMPU) where the IMPUs are typically a URI of several different forms including a SIP URI and a TEL URI. The IMPI and the associated authentication key material is typically stored on a UICC within a profile called an IP Multimedia Services Identity Module (ISIM). During IMS registration, the UE sends the IMPI and a default IMPU to a registrar that queries a Home Subscriber Server (HSS) such that the HSS can generate authentication challenge information and subsequently verify the authenticity of the device through an authentication exchange with the UE's ISIM. Once the authentication has been completed, the HSS typically retrieves the set of IMPUs from the HSS database and informs the UE of these identities. The IMS system then records the relevant routing information so that subsequent service requests to the public identities of the newly registered UE are delivered to the client.
One limitation of the above configuration is that in some applications that rely on IMS, the UE is shared among multiple users. Therefore, the public identities to reach a human user are associated with an IMS device and not associated with the human user of the device. For example, in a public safety network, such as First Responder Network (FirstNet), a UE can be shared between multiple users from an agency across different work shifts. However, it is desirable that a specific user be reachable via a consistent public identity such as a phone number regardless of which UE they are in possession of.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. Those skilled in the art will further recognize that references to specific implementation embodiments such as “circuitry” may equally be accomplished via replacement with software instruction executions either on general purpose computing apparatus (e.g., CPU) or specialized processing apparatus (e.g., DSP). It will also be understood that the terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.